feat: add support for typed events

Syntax:

```ts
interface ServerToClientEvents {
  "my-event": (a: number, b: string, c: number[]) => void;
}

interface ClientToServerEvents {
  hello: (message: string) => void;
}

const socket: Socket<ServerToClientEvents, ClientToServerEvents> = io();

socket.emit("hello", "world");

socket.on("my-event", (a, b, c) => {
  // ...
});
```

The events are not typed by default (inferred as any), so this change
is backward compatible.

Related: https://github.com/socketio/socket.io/issues/3742